The choriocapillaris and photoreceptors depend on the retinal pigment epithelium (RPE) for their function and survival. Thus, regeneration of damaged RPE can influence the status of the choriocapillaris and photoreceptors during chorioretinal disease. This research explores RPE regeneration in situ, focussing on the hypotheses that: 1( there is a structural and functional reorganization of RPE plasma membrane during regeneration; 2) that changes in basement membrane components influence or provide cues for these changes; and 3) that these changes involve the linkage of actin to the plasma membrane, which provides the driving force for the changes in plasma membrane conformation seen during RPE regeneration. An examination of the interactions of plasma membrane, basement membrane and cytoskeleton during RPE regeneration will help explain how RPE function returns to normal, as expressed by the manifestation of structural and functional polarity, e.g., the division of the RPE plasma membrane into domains that segregate functionally important molecules and processes, such as Na-K ATPase and endocytosis sites. The redistribution of these and other plasma membrane components during RPE regeneration will be correlated with changes in basement membrane components and the cytoskeleton. The observations will be made in rabbits that receive sodium iodate i.v. This chemical destroys the RPE over large expanses of the fundus, after which regeneration arises from spared RPE. The regenerating RPE can be conveniently studied in situ by methods for analyzing he structure and function of plasma membranes, basement membranes and the cytoskeleton. This project will use immunohistochemistry, cytochemistry, autoradiography, the freeze- fracture method, morphometry and 3D reconstructions to analyze the redistribution of endocytosis sites, Na-K ATPase and intramembranous particles (including cholesterol binding sites) over the RPE plasma membrane; changes in the basement membrane components fibronectin, laminin, type IV collagen and heparan sulfate proteoglycan; and the reorganization of actin filaments and their linkage to plasma membrane by vinculin. A comparison of these observations with spared RPE in the same specimens and normal rabbits will provide information on how RPE structure and function is restored during regeneration -- and thus its contribution to the recovery form chorioretinal diseases in which RPE regeneration is a component.